Auto blending incredibly slow

Running current version of photoshop on machine with 16gb RAM. Everything else i do is like a rocket but auto blend is terribly slow. I had 15 images in focus stack project but am reduced to stacking 2 at a time Each blend is still taking about 3-5 minutes. Result is excellent, don't get me wrong but i simply can't stack more than 2 without falling asleep waiting.

My images are TIFFS converted from RAW in Lightroom. I'm using a full frame Canon 6D each image after export from LR is approx 114mb.

If i crunch file size down and convert to JPG of course it starts to work, but these are exhibition images and i need quality.

Any suggestions?

Best Regards

Carl from down under